Immunophenotypic differences between plasmacytoma/multiple myeloma and immunoblastic lymphoma.

Four cases of plasmacytoma (PC), six cases of multiple myeloma (MM), and nine cases of immunoblastic lymphoma (IL) of B-cell phenotype were studied with a large panel of monoclonal antibodies applied to frozen tissue sections. There were no significant differences in the immunophenotypes of plasmacytomas and multiple myelomas. However, significant immunophenotypic differences were noticed between the plasmacytoma/multiple myeloma cases (PC/MM) and the immunoblastic lymphoma specimens. The PC/MM cases characteristically stained with alpha (or gamma) and T10 and did not usually stain with mu, leukocyte common antibodies, certain B-lineage antibodies (B1, T015, 4G7, 6A4), or Ia. In contrast, IL sections usually did not stain with alpha or T10 and generally did stain with mu (or gamma), leukocyte common antibodies, B-lineage antibodies, and Ia. Ki-67, an antibody to proliferating cells, stained significantly fewer cells in PC/MM than in IL and stained significantly fewer cells that had a good clinical outcome. We conclude that although no one antibody is useful in distinguishing PC/MM from IL, the application of a panel of antibodies may be helpful in making this distinction. The prognosis may correlate with the numbers of proliferating cells as measured by reactivity with Ki-67.